1. Field of the Invention
The present invention relates to a structure and a manufacturing method of an image TFT array, and more particular, to a structure and a manufacturing method of an image TFT array for an indirect X-ray sensor.
2. Description of the Prior Art
Recently, electronic matrix arrays find considerable application in X-ray image sensors. Such X-ray image sensors generally include scanning lines and data lines transversely and longitudinally spaced apart and across at an angle to one another, thereby forming a plurality of crossover points. Associated with each crossover point is an element or a pixel to be selectively addressed. These elements in many instances are memory cells or pixels of an electronically adjustable memory array or X-ray image TFT array.
A manufacturing method of an X-ray image TFT array according to the prior art includes seven photolithographic and etching processes. At first, the seven processes are concisely described as follows.
The first photolithographic and etching process includes forming a first metal layer and performing a photolithographic and etching process to form a lower electrode and a common electrode;
The second photolithographic and etching process includes forming a first insulation layer (SiNx) and a second metal layer in sequence and performing a photolithographic and etching process to form a gate, a pad, and an upper electrode;
The third photolithographic and etching process includes forming a second insulation layer (SiNx or SiNx/SiOx/SiNx), an amorphous-silicon layer, and a doping layer such as an n+ amorphous-silicon layer in sequence, and performing a photolithographic and etching process to define a semiconductor island;
The fourth photolithographic and etching process includes performing a photolithographic and etching process, especially a photolithographic and wet etching process, to form through holes on a storage capacitor, common electrode, and pad;
The fifth photolithographic and etching process includes forming a third metal layer and performing a photolithographic, a third metal layer wet etching, and a channel etching process, especially a channel dry etching process, to define the third metal layer and the back channel regions of thin film transistors;
The sixth photolithographic and etching process includes forming a passivation layer and performing a photolithographic and etching process to form a through hole on the insulation layer for forming a storage capacitor; and
The seventh photolithographic and etching process includes performing a photolithographic and etching process to form outer test patterns to complete the manufacturing method of an X-ray image TFT array according to the prior art.
Next, the above manufacturing method is interpreted with FIG. 1 to FIG. 6 as follows. FIG. 1 to FIG. 6 are schematic diagrams of a manufacturing method for a thin film transistor (TFT) array 10 for an X-ray image TFT array according to the prior art. As shown in FIG. 1, a substrate 12 is provided. The substrate 12 can be a transparent glass or quartz substrate. Then, a first metal layer (not shown in FIG. 1) is deposited on the substrate 12. A first photolithographic and etching process is performed to remove a portion of the first metal layer to form a lower electrode 16 and a common electrode 18.
As shown in FIG. 2, a first insulation layer 20 and a second metal layer (not shown in FIG. 2) are deposited on the substrate 12 in sequence. A second photolithographic and etching process is performed to remove a portion of the second metal layer to form a gate electrode 24, an upper electrode 26, and a pad 28 on the first insulation layer 20. It is noted that the lower electrode 16, the first insulation layer 20, and the upper electrode 26 constitute a storage capacitor.
Please refer to FIG. 3. A second insulation layer 30, an amorphous-silicon layer 32, and a doping layer 34 are deposited on the substrate 12. A third photolithographic and etching process is performed to remove a portion of the amorphous-silicon layer 32 and the doping layer 34 to define a semiconductor island 36.
As shown in FIG. 4, a fourth photolithographic and etching process, especially a photolithographic and wet etching process, is performed to remove a portion of the second insulation layer 30 and the first insulation layer 20 to form a first through hole 38 on the storage capacitor, a second through hole 40 on the pad 28, and a third through hole 42 on the common electrode 18.
As shown in FIG. 5, a third metal layer 44 is formed on the substrate 12. A fifth photolithographic and etching process, especially a photolithographic and wet etching process, is performed to remove a portion of the third metal layer 44 and an etching process, especially a dry etching process, is performed to form a channel 46 to define the third metal layer 44.
As shown in FIG. 6, a passivation layer 48 is deposited. A sixth photolithographic and etching process is performed to remove a portion of the passivation layer 48 to form a fourth through hole 50 on the storage capacitor. Finally, a seventh photolithographic and etching process is performed to form outer test patterns (not shown in FIG. 6) to complete the manufacturing method of the X-ray image TFT array 10 according to the prior art.
Conventionally, there are as many as seven photolithographic and etching processes. Due to the high number of photolithographic and etching processes, the particle issue produced in the transferring and etching process is more serious. Moreover, since the manufacturing process is complicated, the manufacturing time is longer and the quantity of output is influenced.
U.S. Pat. No. 6,403,965 discloses an X-ray image detector system as shown in FIGS. 7 and 8. FIG. 7 is a plan view of the X-ray image detector system, and FIG. 8 is a sectional view taken along line A-A′ of FIG. 7. The X-ray image detector system comprises a plurality of signal lines 705, a plurality of scanning lines 706, a plurality of pixels 801, a bias line 806, an auxiliary capacity line 702, and an X-ray-to-charge converting part. Each of the pixels 801 comprises a switching element (TFT) 701, a protecting TFT 805, a pixel capacity 703, an auxiliary electrode 704 formed so as to face the pixel capacity 703, and a pixel electrode 707, the signal line 705, the scanning line 706, the bias line 806 and the X-ray-to-charge converting part. Each of the TFT 701, the protecting TFT 805 and the auxiliary electrode 704 is provided with a contact portion 709.
Referring to the sectional view of FIG. 8, the X-ray image detector system includes a glass substrate 201, gate electrodes 202 of the switching element 701 and the protecting TFT 805, the pixel capacity 703. Then, an insulator film 203, an amorphous silicon film 204 and a stopper 205 are deposited. Then, an n+-type amorphous silicon film 206 is deposited. The pixel capacity 703 is connected to a pixel capacity bias 803. Then, a film 207a and a film 207b are deposited to form a protective film 207. After contact holes are formed in the TFT 701, the protecting TFT 805, and the auxiliary electrode 704, a pixel electrode 707 is formed by an ITO (Indium Tin Oxide). A p-type Se film 208 for contact is deposited on the pixel electrode 707, and an Se film 209 is deposited thereon. Then, an Se film 210 is deposited and an n-type Se film 211 is deposited. Thereafter, an Al film is formed as a common electrode 212. Finally, the common electrode 212 is connected to a drive circuit (not shown).
It is noticed that this X-ray image detector system must be protected by the protecting TFT 805 and the film 207b comprising benzocyclobutene (BCB), and the pixel electrode 707 is also a necessary element and must be an ITO layer. In a function as a direct X-ray sensor, the image erase must be performed by irradiation of visible light through the outside of the glass substrate, such that the pixel area must have a transparent section. In case that the pixel capacity 703 is made of a metal material, it takes only a small portion of the pixel area, and a large portion must be left for transparency. While, if an indirect X-ray image sensor only has a small area of storage capacitor, the quality for image acquired will be affected, in addition that an ITO manufacturing process is not required for an indirect X-ray image sensor.